This invention relates generally to D.C. power supplies of the type commonly used in personal computers, for example, to convert commercially available A.C. line voltage to one or more regulated D.C. voltage sources for powering the circuitry of the personal computer. More particularly, the present invention is directed to a circuit for sustaining the operation of such power supplies in the event of a momentary power interrupion on the commercial A.C. line to which the computer or other electronic apparatus is connected. By nature, commercial A.C. line voltage is not entirely stable, for a variety of reasons well understood by those persons having ordinary skill in the art. Power interruptions of various durations are a well documented fact of today's commercial power sources, and a substantial body of prior art is directed to solutions to this problem. The most typical prior art solutions to the problem of power interruption are to install large saturable reactors or large and expensive battery-based uninterruptable power supplies that basically serve as a standby power source in the event of longer term power interruptions. Statistically, however, over 93% of commercial power interruptions are 1 second or less in duration. These seemingly insignificant interruptions can cause data loss and other serious problems in computer systems and other electronic apparatus.
It is therefore a principal object of the present invention to provide circuitry for sustaining the output of a power supply for computers and other electronic apparatus in the event of a momentary interruption in the commercial A.C. power source. It is a further object of the present invention to provide such circuitry in a configuration that is inexpensive and that may be easily added to existing personal computer power supplies. These and other objects are accomplished in accordance with the illustrated embodiment of the present invention by providing a capacitor bank and associated charge path, discharge path, and disconnect circuitry connected across the raw D.C. voltage source internal to a personal computer that is derived by rectifying and filtering the commercial A.C. line voltage powering the personal computer. During stable operation of the commercial A.C. power source the integrated capacitor bank is maintained in a charged condition. When an interruption occurs in the commercial A.C. power source, the energy stored in the capacitor bank is discharged to maintain the raw D.C. voltage source and to thereby sustain operation of the computer for up to one second while the commercial A.C. power source stabilizes.